E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Those who took part in the coup détat which effected the fall of Robespierre, with the desire of restoring the legitimate monarchy. So called because the Reign of Terror was brought to an end on the ninth Thermidor of the second Republican year (July 27th, 1794). Thermidor or Hot Month was from July 19th to August 18th. (Duval Souvenirs Thermidoriens.)